There is increasing need for extremely pure hydrogen peroxide in both the electronics and food industries, particularly in the electronics industry. High purity hydrogen peroxide is also used in alkaline systems and neat for etching applications.
Because of the exacting requirements of such applications, hydrogen peroxide must meet stringent purity requirements such as those set by the semiconductor industry, being substantially free of metallic and other elements that might contaminate the semiconductor workpiece or interfere with the cleaning or etching functions. Accordingly, the semiconductor industry has recommended standards which include limits on the maximum permissible concentration of over 30 individual chemical elements and on the total amount of residue left on evaporation. Common objectionable chemical elements are sodium, aluminum, phosphorus and tin. It is also general practice in the industry to pass the hydrogen peroxide through a 0.2 micron filter to remove particulate material, a time-consuming and costly step considering the filter is fine enough to screen out many colloidal materials.
Hydrogen peroxide as manufactured normally contains chemical impurities, although in low concentrations, such as Na, Pd and P, the latter usually as phosphate ion. Also since hydrogen peroxide is corrosive to many of the metallic materials of construction, it may become further contaminated in storage and transport by such common corrosion products as Fe, Cu, Mn and Cr, which are well-known catalysts for the decomposition of hydrogen peroxide. The peroxide can also become contaminated with decomposition catalysts when diluting concentrated solutions with other than multiple-distilled or deionized water.
To meet the increasing demand for high purity hydrogen peroxide, the chemical industry uses various techniques including distillation and ion-exchange-resin technology to purify (remove undesired ions) the hydrogen peroxide. Each method has its advantages and disadvantages. For example, in the case of ion exchange, certain metal ions such as sodium, iron and calcium can readily be removed by using cation exchange resins. However, some metals are not readily removed by this process because they are present as anionic complexes.
Processes are also known in the art for removing anions. U.S. Pat. No. 3,294,488 teaches using a quaternary ammonium polystyrene resin to purify hydrogen peroxide. Kawaguchi et al. (JP No. 61-28296) teach using a pyridine type anionic resin with a cationic resin to produce high purity hydrogen peroxide. Yield and purity loss due to the reactivity of the peroxide with the alkaline exchange resins and potential for explosions in the ion exchange column are limitations on these ion exchange processes.
The present development of employing reverse osmosis to purify the hydrogen peroxide avoids the yield and purity loss and safety hazard limitations present in some other purification processes.
Reverse osmosis is an easy-to-operate system that has been used extensively to purify drinking water and to concentrate materials by removing water. It has been used in the electronics industry to produce ultra-high purity water. The water passes through the membrane in these applications resulting in purified water as the permeate and in the materials in the feed water being concentrated as the concentrate. Developments in membrane technology have produced systems that meet the most stringent requirements for water purity in these applications.
Reverse osmosis has not been known to be used to purify solutions in water such as hydrogen peroxide, which typically is 5 to 50 weight percent hydrogen peroxide in water. To remove impurities from the hydrogen peroxide solution, both the water and the hydrogen peroxide, not just the water, must permeate the membrane while leaving the impurities behind.
Reverse osmosis membranes are generally known to be sensitive to attack by chemicals such as hydrogen peroxide, which is strongly oxidative particularly at high concentrations (greater than 25 weight percent). The only membrane hydrogen peroxide application known is in hydrogen peroxide solution analyzers (See U.S. Pat. No. 4,525,265 and Japanese Publication Nos. 5 7122-797, 8 1048-159, and 5 8129-245-A, for example), where the flow rate through the membrane and the concentration of the hydrogen peroxide are low and breakthrough of impurities generally is not critical.